As commerce and industry advance, the number of densely populated cities increases, and the air pollution caused by human activities becomes increasingly worse. In recent years, the air pollution due to the exhaust gas discharge of automobiles and motor cycles, massive petroleum consumption, and dispersion of various different harmful air pollutants jeopardizes the health of people who have been living in the air polluted environment for a long time, and thus people pay more attentions to the air quality of the environment.
On the other hand, viruses, bacteria and toxic dusts directly affecting our health are always our major concerns, and people attempt using a filter material to isolate viruses and bacteria, so that the viruses and bacteria cannot enter our breathing system or cause infections. At present, most filters are filter nets made of stacked fibers, such as a multi-layer filter net with a substrate made of polypropylene (PP), and filter layers of this type are applied to the manufacture of masks, face masks, nose filters or breathing apparatus.
Masks are generally divided according to their applications into dust masks, activated carbon masks and medical N95 masks certified by National Institute for Occupational Safety and Health (NIOSH). The N95 mask comes with a dense fiber structure capable of isolating 95% of tiny particles having a size over 0.3 μm), and thus the N95 mask provides a better protective effect than the dust mask and activated carbon mask.
In general, bacteria having a diameter of over 0.3 μm can be isolated by the N95 mask easily as shown in Table 1, but viruses with a nanoscale diameter (which is much smaller than the bacteria with a micro diameter) cannot be isolated by the N95 mask. For example, the virus of severe acute respiratory syndrome (SARS) has a diameter of 100˜120 nm only and the N95 mask is unable to effectively isolate or prevent the SARS virus from passing through the mask.
TABLE 1DiameterType(μm)Related DiseaseVirusOrthomyxoviridae0.08~0.12Influenza Types A, B and CCoronaviridae0.10~0.12SARSBacteriaSerratia Marcescens1.0~5.0Nosocomial InfectionsMycobacterium0.45TuberculosisTuberculosis
Therefore, a conventional filter structure manufactured by a fiber stacking technology just has a protective effect up to a micron scale, but almost has no effect for viruses in a nanoscale.
Relatively, the filter can limit the size of transmitting particles, and thus a refined filter structure may give rise to an uncomfortable breathing pressure to users. In other words, the smaller the aperture ratio of the filter material, the lower is the level of ventilation. As a result, users have difficulties inhaling or exhaling normally through the filter material.